About 40 years ago, Palm Beach County farmer John Thomas was tending 2,500 acres south of Buffalo, N.Y., some of it land bought and cleared by his father at the turn of the century. Thomas and his family grew tomatoes, beans, strawberries and raspberries, which they sold to area stores.

During the 1950s, Thomas began to notice a change in the marketplace.

``The produce and the supply in canned goods was beginning to come from different areas that had lower cost of production, and that was shrinking our margin,`` he said.

In 1958, recognizing that he would be unable to compete in the long run with produce trucked in from other parts of the country, Thomas shifted the base of his livelihood to Florida, renting about 800 acres of Palm Beach County farm land.

Today, Thomas, 70, oversees a 6,500-acre farm operation in Florida with annual sales of about $40 million. A farm trade publication lists him as one of the top 100 vegetable growers in the United States.

Despite his success, Thomas says he`s experiencing a mild case of deja vu these days. He says he`s getting the same kind of inklings he felt in the 1950s.

The reason: The prospect of a free-trade agreement between the United States and Mexico.

Thomas, like many other South Florida farmers, grows tomatoes, peppers, cucumbers, eggplant, beans and strawberries.

These crops -- along with fresh citrus, processed citrus, carrots, lettuce, squash, mangos, melons, cattle, grains, sugar, spices, tobacco and oilseed -- compete directly with crops grown in Mexico, according to a recent study done at the University of Florida.

The United States has tariffs in place that help protect the value of most of Thomas` crops, along with much of Florida`s $6.2 billion-a-year agricultural industry. But U.S. officials are working on a Mexican free-trade pact that would reduce those tariffs or eliminate them entirely over time.

The long-term objective is to create a North American free-trade area encompassing the United States, Mexico and Canada. The result would be the world`s largest market, with annual production of $6 trillion and more than 360 million people, trade officials say.

``If we can grow the global pie, Florida will benefit,`` U.S. Trade Representative Carla Hills told state agricultural leaders in Palm Beach Gardens two months ago.

The free-trade talks began June 12 in Toronto. While working groups are continuing to meet, the next meeting of the trade representatives of the three nations is tentatively scheduled for Aug. 18-19 in Seattle.

While no timetable has been set for the conclusion of the talks, it doesn`t seem likely they will drag on too long.

``We`d hope to conclude them by next year,`` said Timothy O`Leary, spokesman for Hills` office.

It is too soon to know what kind of agreement the talks will produce and to what extent the interests of Florida farmers will be safeguarded.

``We`ll take however long it takes to negotiate a good agreement for the United States,`` O`Leary said.

Officials at the state Department of Agriculture aren`t panicking.

Hills has promised state Agriculture Commissioner Bob Crawford the chance to provide some input as talks get rolling, said Bob Blankenship, an Agriculture Department spokesman.

``We feel fairly comfortable at this time that we`re going to have a voice, in one form or another, whatever the final agreement turns out to be,`` Blankenship said.

IMPACTS ON FLORIDA

Despite assurances Crawford may have received, there was little consolation held out to Florida farmers at Hills` Palm Beach Gardens appearance in May.

``I can`t fight all the fears,`` Hills told farmers. ``You don`t care what might be, you`re so worried about what could be.``

Yet Florida farmers continue to be worried about what could be.

And two studies that address the potential impact of free trade with Mexico on Florida farmers lend some justification to their worry.

While efforts to open up trade are being pursued on a number of fronts -- most broadly at the General Agreement on Tariffs and Trade talks, which have been going since 1947 -- the impending pact with Mexico looms as the single greatest threat to Florida farmers, says a study on the economic impacts of agriculture in the Agricultural Reserve Area of Palm Beach County.

``The serious threat to vegetable and citrus producers comes from a possible bilateral free-trade agreement between the United States and Mexico. Elimination of tariff protection for domestic orange juice would wreak havoc with the competitive position of Florida orange growers. Reduction of tariff protection for other citrus varieties would also lead to significant increases in Mexico`s share of U.S. markets,`` said the study, prepared last winter by Dames & Moore, a consulting firm with offices in Boca Raton and Tampa, and the Institute of Food & Agricultural Sciences at the University of Florida.